1. Field of the Invention
The present invention relates to an optical integrated circuit applied to an optical data processor such as an optical computer.
2. Description of the Related Art
Recently, it becomes more important to transmit and process informational data. Especially, data transmission and data processing using light are thought as an important technology because light can travel fast. An optical integrated circuit is a kind of device which processes information consisting of light. The optical integrated circuit can be made small by employing optical waveguides. Such optical integrated circuits can be produced on a large scale by utilizing semiconductor manufacturing processes, that enable production of the optical integrated circuits at low cost.
Light signals are processed in such an optical integrated circuit, and are finally converted into electric signals. Referring to FIG. 5, a light detector of a conventional optical integrated circuit is illustrated. FIG. 5 schematically shows a cross sectional view of an optical integrated circuit 39 having a light detector 38. A p-type region 32 doped with p-type impurities is formed in a surface region of an n-type silicon substrate 31. The p-type region 32 and the n-type silicon substrate 31 form a pn conjunction. An electrode 33 and an electrode 34 are respectively connected with the p-type region 32 and the
n-type silicon substrate 31. The light detector 38 consists of a part of the n-type silicon substrate 31, the p-type region 32, the electrode 33 and the electrode 34. A buffer layer 35 is formed on the n-type silicon substrate 31. An optical waveguide 36 is formed on the buffer layer 35 and the p-type region 32, and the optical waveguide 36 is directly in contact with the p-type region 32.
Light 37 travels in the optical waveguide 36. When the light 37 reaches above the p-type region 32, a part of the light 37 is absorbed by the p-type region 32. The light absorbed by the p-type region 32 is converted into electric signals, and the electric signals are detected through the electrode 33 and the electrode 34.
In the optical integrated circuit 39 having the light detector 38, light sensitivity of the light detector 38 depends on the length 1 of the p-type region 32. The length 1 must be long enough to receive much of the light 37 so that the light detector 38 has the sufficient light sensitivity for practical use, for example, to obtain a sufficient signal. However, as length 1 is elongated, the light detector 38 is more influenced by stray light in the optical integrated circuit 39. Such stray light degrades a signal-to-noise ratio of the light detector 38.
The present invention overcomes the above mentioned shortcomings associated with the conventional optical integrated circuit and provides an optical integrated circuit having a light detector with high sensitivity and good signal-to-noise ratio.